1. Field of the Invention
The present invention relates to a self-adjustable universal spanner and, more particularly, to a self-adjustable universal spanner employing a size enlarger capable of changing a dimension of the spanner in order to fasten or unfasten various bolts and nuts having different diameters.
2. Description of Related Art
Conventionally, spanners for fastening or unfastening bolts and nuts may be classified into a general spanner set, a ratchet spanner set, a monkey spanner, and so on. The general spanner set is comprised of a plurality of spanners having different sizes so that they should perform repeated operations of insertion and separation into/from bolts and nuts, thereby making a user perform troublesome operations. The ratchet spanner set includes a ratchet handle for continuously operating the spanner, and sockets having various sizes inserted into the ratchet handle. The monkey spanner can adjust its size by rotating a screw to accommodate various sizes of bolts and nuts; however, it is also troublesome to operate the spanner due to repeated insertion and separation.
In addition, in the case of the conventional ratchet spanner set, since the ratchet handle is operated spaced apart from a bolt by a large gap due to the socket inserted into a head of the bolt, a user should use one hand to grip the ratchet handle and the other hand to grip the socket on the bolt head in order to perform a stable operation. Further, the general spanner set and the monkey spanner also require using both hands to prevent the bolt head from separating from the spanner.
Moreover, the conventional spanners should have a plurality of spanners or sockets corresponding to sizes of bolts and nuts. Therefore, when any one of the tools is lost during the operation, the operation may be stopped due to the lost size. In addition, due to inconvenience of storage and management of numerous parts, it is very difficult to use the conventional spanners in dangerous environment such as a high attitude and so on.
In order to solve the problems, spanners disclosed in U.S. Pat. Nos. 6,202,516 and 6,945,143 have been proposed. However, the spanner of '516 patent has a structure that a bracket is installed at an outer surface of the spanner head to prevent a ratchet member and a size adjustment member from retracting and separating from a slide groove, still remaining problems such as lack of durability and inconvenience of use. In addition, in the spanner of '143 patent, a semi-circular projection of a ratchet and side-adjustment member is inserted into a semi-circular slide groove formed at an upper jaw of a spanner head to be securely slid along the groove, a sloped surface of the adjustment member is in contact with a bottom surface of the slide groove of the spanner head, and an upper surface of the adjustment member is in contact with a sloped surface of the upper jaw of the spanner head, thereby making the adjustment member turn over to prevent retreat of the adjustment member. However, an angle between the bottom surface of the lower jaw of the spanner head and the bottom surface of the slide groove has a range of 147±3° due to small friction therebetween, thereby accommodating only two or three sizes of bolts. In order to accommodate more sizes, the head should have a larger size, and the ratchet and size-adjustment member should be larger, thereby generating problems such as lack of durability and bolt braking.